1. Field of the Invention
The present invention relates to a waste treatment system and method and more particularly to a waste treatment system and method for anaerobic fermentation of animal excreta for conversion into combustible gases and fertilizer.
2. Description of the Prior Art
A large portion of underground water table pollution results from animal waste seepage, particularly in the warmer western and southern parts of the United States where there are larger concentrations of animals in small spaces, such as in dairy operations. Excreta from dairy cows is usually gathered in a relatively small area, and the liquid portion simply seeps down into the undergound water table.
Animal waste contains many elements which make it an ideal fertilizer, in addition to which the methane and other gases present are useful as a source of energy. However, prior art systems for converting the animal wastes to combustible gases and fertilizer have been ineffecient and uneconomical. For example, composting requires considerable labor and is not complete for approximately twelve months. Moreover, recovery of the methane gas produced during the composting process is dangerous because of the explosiveness of the gas in the presence of air.
My issued U.S. Pat. No. 4,008,689 discloses a reasonably effective system for converting animal excreta into useful combustible gases and fertilizer without polluting rivers and underground water. In that system the animal excreta is received in a trough and contained for a period of time sufficient to allow a predetermined portion of the excreta to become liquified. This is transferred to a fermentation tank, and the excreta is next pumped out after fermetation is completed. Although the system is a significant advance over the prior art, the air initially present in the fermentation tank present a potential danger of explosive combination with the methane generated in the process. The system was also characterized by significant items of cost, such as the tank and the means for withdrawing materials from the tank.